While this invention relates generally to heat exchangers, it more specifically involves flexible heat exchangers that can be conformed to the outer cylindrical surface of tanks or the like. For example, wine vats are closely controlled in temperature, which is usually accomplished by circumferentially attaching a stainless steel jacket (heat exchanger) to the outer surface of the tank and pumping cooled fluids through the jacket. Since the stainless steel jacket is metal, a great deal of rime ice forms on its outer surface.
Although the stainless steel jackets work, their cost is substantial and the condensation of rime ice is a continuing problem. Also, they are difficult to install, and cannot be easily brought into integral contact with the surface of a cylindrical tank, even when custom made. In addition, these jackets usually have relatively high pressure drops across the inlet and outlet, resulting in high energy consumption in the pump transfer system circulating the heating or cooling fluid.
The good insulating characteristic of plastics is a drawback for their use in heat exchange elements. However, by using polyolefins, such as polypropylene and polyethylene, for the novel heat exchanger of this invention and designing it with large flat contacting surfaces, plus a high capacity flow rate of cooling or heating fluids on the opposite side of the thin plastic contacting surface, most of the prior problems of plastic heat exhangers have been minimized. The foam insulation adhered to the exterior surface eliminates the rime ice because it is sealed to the outer sheet forming the exchanger element so that no moisture-laden air can contact this surface. As a result, there is no condensation on this surface or on the exterior surface of the foam due to its insulating characteristics.
Economically, the heat exchangers according to this invention cost less than one-sixth of the prior art stainless steel jackets, and are much more easily conformed to the surface of a tank due to the flexibility of the plastic. Because it is constructed of plastic, the novel heat exchanger can be "stretched" slightly to fit properly when installed on a cylindrical surface, thereby ensuring positive contact with a tank or other cylindrical surface over the entire surface area where thermal heat exchange is to be accomplished.
Many factors determine the efficiency of heat exchangers, but with the innovations employed in this invention and the features achieved, this plastic exchanger rivals the prior art stainless steel jacket in efficiency. This is a totally unexpected result for a plastic exchanger.
Manifolds are specially designed for high flow rates and are securely connected to the thermal exchange portion so that a complete heat exchanger modular unit can be fitted to a surface by holding the manifolds with clamps or the like and stretching the unit slightly under tension across a cylindrical surface through adjusting bolts on the clamps. As the insulating foam is bonded only to an outer surface sheet of modular units, it is not placed under tension by this action. Further, the thickness of the thermal exchange is less than one-quarter inch (excluding the thickness of the foam insulation), which allows it to be conformed easily to cylindrical surfaces with diameters of over three feet without placing undue stress on its internal structures.
Polyolefins are non-corrosive, non-scaling and chemically inert, making this novel heat exchanger useful in corrosive and caustic environments. However, very strong oxidizing acids can cause slow oxidation, and organic solvents at temperatures of about 180.degree. F. may cause some deterioration. Thus due to the construction and the characteristics of polyolefins, this novel heat exchanger has service temperatures from -40.degree. F. to +300.degree. F., and is useful with corrosive fluids of nearly all types.